Document jsvm timeout

[alephnull]

This parameter was fixed in 2.5.1.

Document that:

• these are not hard timeouts
• searchable with the error message JS middleware timed out after + tyk
• applies to virtual endpoints as well as jsvm

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[joshblakeley]

not stale